1. Field of the Invention
The present invention relates generally to data transmission apparatuses, and more particularly, to a data junction and branching mechanism for an asynchronous data transmission path.
2. Description of the Background Art
Data processing apparatuses such as data flow type information processors employ asynchronous data transmission paths. In such a data processing apparatus, a junction mechanism for merging a plurality of packet data is used for transmitting packet data applied from data transmission paths in a plurality of preceding stages to a data transmission path in one succeeding stage. For transmitting packet data applied from a data transmission path in a preceding stage to data transmission paths in a plurality of succeeding stages, a branching mechanism for sequentially branching the respective packet data is used. A junction and branching mechanism including a junction mechanism and a branching mechanism is used for transmitting each of a plurality of packet data applied from data transmission paths in the plurality of preceding stages to any of data transmission paths in the plurality of succeeding stages.
FIG. 7 is a block diagram showing a conventional data transmission apparatus for merging a plurality of packet data applied from transmission paths in two preceding stages to a transmission path in one succeeding stage. Such a data transmission apparatus is disclosed in Japanese Patent Laying-Open No. 62-265738 corresponding to U.S. patent application Ser. No. 260,068, now issued as U.S. Pat. No. 4,985,890.
An n-bit packet data applied from an A port is transferred to a data transmission path 170 through data transmission paths 110, 120 and 130. An n-bit packet data applied to a B port is transferred to data transmission path 170 through data transmission paths 140, 150 and 160. When the packet data from the A port and the B port arrive at the transmission paths 130 and 160 nearly simultaneously, the one packet data having arrived prior to the other is first transferred to data transmission path by the control of an arbitration control portion 220.
Operation will be described in a case where packet data from the A port arrives prior to packet data from the B port.
Packet data is applied to data transmission path 110 in response to a transmission signal C110. As a result, a transmission acknowledging signal AK110 enters the inhibiting state. When a transmission acknowledging signal AK120 is in the permitting state, the packet data is transferred to data transmission path 120 in response to a transmission signal C120. As a result, the transmission acknowledging signal AK120 enters the inhibiting state. When a transmission acknowledging signal AK130 is in the permitting state, the packet data is transferred to data transmission path 130 in response to a data transmission signal C130. As a result, the transmission acknowledging signal AK130 enters the inhibiting state.
Arbitration control portion 220 sets a transmission acknowledging signal AK171 to the permitting state and a transmission acknowledging signal AK172 to the inhibiting state in response to the transmission signal C130 and the transmission acknowledging signal AK130 when a transmission acknowledging signal AK170 is in the permitting state.
Meanwhile, packet data is applied to data transmission path 140 in response to a transmission signal C140. As a result, a transmission acknowledging signal AK140 enters the inhibiting state. When a transmission acknowledging signal AK150 is in the permitting state, the packet data is transferred to data transmission path 150 in response to a transmission signal C150. As a result, the transmission acknowledging signal AK150 enters the inhibiting state. When a transmission acknowledging signal AK160 is in the permitting state, the packet data is transferred to data transmission path 160 in response to a transmission signal C160. As a result, the transmission acknowledging signal AK160 enters the inhibiting state.
With the transmission acknowledging signal AK171 being in the permitting state and the transmission acknowledging signal AK172 being in the inhibiting state, data transfer from data transmission path 130 to data transmission path 170 is permitted and data transfer from data transmission path 160 to data transmission path 170 is caused to stand by. After the packet data is transferred from data transmission path 130 to data transmission path 170 response to a transmission signal C171, the transmission acknowledging signal AK172 enters the permitting state to transfer the packet data from data transmission path 160 to data transmission path 170.
FIG. 8 is a block diagram showing a conventional data transmission apparatus in which packet data applied from a transmission path in one preceding stage is branched out into transmission paths in two succeeding stages in turn. This data transmission apparatus is disclosed in Japanese Patent Laying-Open No-62-265740 corresponding to U.S. patent application Ser. No. 259,850, now issued as U.S. Pat. No. 5,133,054.
Packet data applied to a data transmission path 180 is transferred to either a data transmission path 200 or 210 through a data transmission path 190 and output to a C port or a D port.
Packet data is applied to data transmission path 180 in response to a transmission signal C180. As a result, a transmission acknowledging signal AK180 enters the inhibiting state. When a transmission acknowledging signal AK190 is in the permitting state, the packet data is transferred to data transmission path 190 in response to a transmission signal C190. As a result, the transmission acknowledging signal AK190 enters the inhibiting state.
Meanwhile, a branch destination specifying bit BR previously applied to a comparison and determination portion 230. Each packet data includes an identifier. Comparison and determination logic portion 230 compare an identifier included in packet data with the branch destination specifying bit BR and applies the comparison result to a branch control portion 240. Branch control portion 240 activates either of activation signals EA or EB according to the comparison result.
Firstly, it is assumed, for example, that the activation signal EA is activated. In this case, when a transmission acknowledging signal AK200 is in the permitting state, packet data is transferred from data transmission path 190 to data transmission path 200 in response to a transmission signal C200. Conversely, it is assumed that the activation signal EB is activated. In this case, when a transmission acknowledging signal AK210 is in the permitting state, packet data is transferred from data transmission path 190 to data transmission path 210 in response to the transmission signal C200.
A junction and branching mechanism is structured by connecting the data transmission apparatus shown in FIG. 8 to the succeeding stage of the data transmission apparatus shown in FIG. 7.
The total performance of the junction and branching mechanism with the data transmission apparatuses shown in FIGS. 7 and 8 connected in series is limited by maximum flew rate of packet data merged in transmission path 170. Mere specifically, the performance of packet data input is allowed only up to the maximum flow rate of data transmission paths 170, 180 and 190 through which the merged packet data flow.
When packet data are to be simultaneously input to a plurality of data transmission paths on the input side, packet data can not be input to each data transmission path at the maximum flow rate of its data transmission path. As a result, a flow rate of input packet data is inevitably reduced. In a case of merging of packet data from n ports, for example, a flow rate of packet data which can be input to each pore is reduced to 1/n. In this case, a buffer should be provided.